Automated shift transmissions are increasingly used in both the passenger car and commercial vehicle sectors, since while having relatively low weight, compact dimensions and high transmission efficiency, thanks to their automated shift processes, they offer greater operating comfort and reduce the fuel consumption of the motor vehicle concerned.
A disadvantage in shift transmissions, however, is the structure-entailed interruption of the force flow between the drive motor and the drive axle connected with the output shaft of the transmission during a gear change, which occurs because the engine coupling is temporarily disengaged and the shift transmission is briefly in its neutral position. During an upshift, especially an upshift in traction while driving uphill, this can result in an undesired deceleration of the motor vehicle and, during a downshift, especially a downshift while coasting downhill, to an undesired acceleration of the motor vehicle. In general this leads to a delay and to an uncomfortable course of the shift process.
For that reason, particularly in the case of commercial vehicles and to shorten the force interruption, it is known to accelerate synchronization of the respective gear to be engaged in an upshift by way of a transmission brake or, with the engine clutch engaged, by acting on the control of the engine by way of an engine brake, but this entails greater cost and complexity for the additional equipment.
Accordingly, the present invention relates both to a simple automated gearbox as used mainly in passenger cars and light transport vehicles and to range-change transmissions consisting of more than one serially coupled, part-transmission as used mainly in heavier commercial vehicles. For example, in DE 100 51 354 A1, a range-change transmission is described, which consists of a simple main gearbox made as an intermediate gear structure and a range group downstream therefrom in the form of a simple planetary gearset.
Against that background, the purpose of the present invention is to further develop an automated gearbox of the type mentioned earlier in a simple and space-saving way and in such a manner that during a shifting process the interruption of the traction force can be avoided.
In addition, a method for controlling the gearshifts of such an automated gearbox is indicated.
The solution of the objective relating to the automated gearbox consists of a controllable friction clutch, which is provided as a change-under-load clutch for connecting the input shaft directly to the output shaft, as necessary.